IPv6 routing /48s

Michael Sinatra michael at rancid.berkeley.edu
Mon Nov 17 23:20:56 UTC 2008

On 11/17/08 14:46, Robert.E.VanOrmer at frb.gov wrote:

> ARIN claims they are seeing /48s routed, at least in their route tables. I 
> have seen some new momentum on the allocation of /32's, don't know if that 
> is in response to rules like this??  Would be awefully difficult for our 
> organization to come up with the rationale to need 65K /48s internally to 
> justify a /32.

You may want to post this issue to the ARIN PPML list (see 
http://www.arin.net/mailing_lists/index.html if you're not already 
subscribed), as that might be a useful venue for discussion as well.

You're right in noting that this is a catch-22.  ARIN and other RIRs are 
now giving out PI /48s, but there is still a notion that /32 is 
considered the maximum routable prefix length.  However, UCB sees a lot 
of globally-routed /48s (and /35s, /40s, etc.) in our DFZ routing table. 
  (I also see some /48s disaggregated from a /32 and announced in at 
least one non-ARIN region, but I am sure this is happening elsewhere. 
:-( )  So, I do think that /48 is beginning to be the new /32 when it 
comes to prefix filtering, but I can also understand those who want to 
hold to the more strict IPv6 filtering policies.

I think in the end, we are going to end up generally accepting up to 
/48s.  Basically, we're going to break the routing table anyway--the 
number of potential /32s is more than enough to do that, and forcing 
everyone who:

a. needs to be multi-homed; and
b. needs more than 1-2 subnets

to get a /32 has to be a waste, no matter how big the potential address 
space is overall.

One compromise would be to require that blocks that can be aggregated be 
aggregated, and then allow PI /48s.  In theory, this could be enforced a 
number of ways, but I am sure we're all aware of how well that works...


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